Nadja Ensink-Teich with her daughter Fleur. The family had been living in north London.
Photograph: Judith Jockel for the Guardian

Hugging her two-year-old daughter, Fleur, Nadja Ensink-Teich turns the pages of the small photo book. “Papa”, Fleur says excitedly, pointing to a picture of her father, Dr Jeroen Ensink, cradling her as a newborn on the sofa of their London flat 11 days after her birth.

“This one was taken just one hour before he went out,” says Nadja. “I’ve kept the outfit Fleur was wearing. This is his watch,” she says, stretching out her arm. “I wear his wedding band. And this is the ring he wanted to buy me for when Fleur was born. I had to buy it myself … that was so hard,” she adds in barely a whisper.

It is more than two years since Jeroen, 41, a world-renowned public health academic at the London School of Hygiene and Tropical Medicine, was stabbed to death on 29 December 2015 by Femi Nandap, 23, a Nigerian student in the grip of a severe psychotic illness. Jeroen, from Zwolle in the Netherlands, had popped out from their Islington flat to post cards announcing his daughter’s birth.

Ever since, Nadja, 39, has been in limbo. “I still have no answers,” she says, furious at the “gross insensitivity” of the police and the Crown Prosecution Service (CPS), and procedural delays that have delayed his inquest, now due in July.

It will, she hopes, answer the question of why, six days before Nandap killed Jeroen, charges against him relating to an incident seven months previously, when he was acting strangely with a knife and assaulted a police officer during an arrest, were dropped.

Jeroen Ensink, a public health academic, and Fleur. The photo was taken one hour before he was killed. Photograph: Judith Jockel for the Guardian

The Guardian has learned that an investigation by the Metropolitan police directorate of professional standards highlighted several lost opportunities to identify Nandap’s mental health issues before the killing, and his sister twice flagged that he was experiencing paranoia and hallucinations due to heavy cannabis use.

Yet a report from Merlin – the system the Metropolitan police service uses to record and share information on vulnerable people – was not created. It would have highlighted Nandap’s mental health problems, possibly meaning he would have received help before he killed. The DPS now recommends the MPS change its policy on Merlin completion to make it mandatory, not just best practice, in such cases.

Instead, after his arrest in May 2015, Nandap was granted bail, which he breached by returning late from a visit to Nigeria, where he underwent mental health treatment. On returning to Britain and being rearrested, he was again freed on what Nadja believes were lax bail conditions.

On 23 December 2015, charges were dropped by the CPS for “insufficient evidence”. Six days later, Jeroen was dead.

Nadja left their north London flat, unable to look daily at the spot on their doorstep where Jeroen was killed. She packed up and drove herself back to the Netherlands, with Fleur in a baby seat and her husband’s ashes stowed underneath it. “I look back now and I have absolutely no idea how I managed that journey,” she says. She moved to a quiet road in a small Dutch town, avoiding new-build estates “full of happy young families, which I just could not cope with”.

As a full-time mother, giving up a career as an event manager, she would have been living close to her supportive parents. But her mother, Henriëtte, died aged 75 after a short illness on 1 January, two days after the second anniversary of Jeroen’s death.

Photos of Jeroen are everywhere in the house; above Fleur’s bed, which she kisses each night, above her changing mat, ensuring he looked down on her from her earliest memory. Mother and daughter light a “candle for daddy” at dinner time. “He is here. He is part of our daily lives.

“There are moments, and I had one this morning, when I look at these pictures and I’m like ‘I can’t believe you are not here’,” Nadja says.

Fleur knows the concept of a dad. “She is way too young to understand she doesn’t have one and others do. I dread the moment when she asks ‘Where’s dad?’ and I have to explain,” her mother says.

“When she does start asking questions, the last thing I want to say to her is ‘I don’t know’.”

Eighteen months after Jeroen’s death, three Met officers turned up in the Netherlands. They had begun an internal investigation. Nadja was flabbergasted they had only just instigated one, because she had made a very vocal call at the Old Bailey, as part of her victim impact statement, for a full investigation when Nandap was sentenced to an indefinite hospital order, having pleaded guilty to manslaughter through diminished responsibility in September 2016.

Denied legal aid, forced to resort to crowdfunding for her legal fees, Nadja says the officers told her it was not necessary for her to have a lawyer. “But it is three parties: it’s us, it’s the CPS, it’s the police. So, why do they come along and tell me I don’t need a lawyer when they will have a QC?”

Pictures at Nadja’s home. She says: ‘It is my responsibility to give Fleur a carefree childhood.’ Photograph: Judith Jockel for the Guardian

Without a lawyer, she would have been overwhelmed. “I would probably have ended up as this mad, angry widow nobody wants to talk to because it’s the only thing on her mind. It would have deprived Fleur of a mother when she had already lost her dad,” she says.

The CPS response also infuriated her. It has said that even if charges had not been dropped, Nandap, who had no previous convictions, would still have been granted bail. She feels as though they are saying it was Jeroen’s fate. “That is for the inquest,” she says. “It is totally the wrong thing to say at the time, and to stick to it too. Why were the charges dropped?”

It has been “like a battlefield, sadly, like David and Goliath”. Delays are racking up legal fees, now likely to be more than her original target, but she is grateful to those who have answered her crowdfunding appeal, without which, she says, she would have been lost. She has made formal complaints about the MPS.

She has tried to access a letter from Nandap’s family to the court, which she wants for when Fleur is older. “Whether she will want to read it, whether it will help her or not, I do not know.” She is aware that the passage of time makes it harder to retrieve such documents and her duty is to get it now.

The photo book is full of pictures taken of father and daughter in their too short shared lifetime. “Jeroen was always saying to me that I took too many pictures. But I am so glad that I did,” she says.

For his widow and daughter, he lives on in those photographs, as he does through the scholarship now awarded in his memory.

“I made a promise to Jeroen, in my heart to him, that I am not going to be hard, I’m not going to be bitter. It is my responsibility to give Fleur a carefree childhood. I still remember the moment I made it, on that sofa, on that afternoon [of his death]. Throughout these two years, I keep repeating it to myself,” she says.

“When Fleur is old enough, I want her to know that I did absolutely everything I could. I see that as my responsibility to her, and to Jeroen.”

An MPS spokesman said the inquest would review police contact prior to Dr Ensink’s death and it had voluntarily referred itself to the Independent Office for Police Conduct, and subsequently received an official complaint from his family.

He said: “A Directorate of Professional Standards investigation concluded there were no misconduct matters but areas of learning have been identified for the MPS and work is under way to implement this.

“The MPS is fully supporting, and will continue to fully support and cooperate with, the coronial process. We understand Mrs Ensink-Teich’s desire for answers and want to provide them for her, and her family.”